Method and device for condensing CO2

ABSTRACT

The invention relates to a method and to a device for condensing CO2 or CO2 separation. According to the invention the thermoacoustic effect is used, with the aid of waste heat from a power station, to produce power for a compressor for compressing a working medium, in particular for compressing a CO2-containing flue gas, and/or for cooling the working medium.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German application No. 10 2008 018 000.9 filed Apr. 9, 2008, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to a method and to a device for condensing a working medium, in particular for condensing CO2.

BACKGROUND OF THE INVENTION

Various methods are known for reducing the CO2 emissions of power stations in which CO2 is separated from the fuel gases or flue gases of the power station in order to then separately accumulate or store the CO2. Separation is necessary as the waste gas from the power stations is made up to only a relatively small extent of CO2: the bulk of it is nitrogen, which the ambient air contains in addition to oxygen. As it is not expedient to store the harmless nitrogen geologically, the CO2 must firstly be separated from the nitrogen and possibly other substances contained in the waste gas, such as sulphur oxides (SO_(x)). Examples of separation methods would be absorption methods using liquid solvents, solids adsorption, membrane methods and high-temperature methods.

To render the separated CO2 transportable and to be able to store it, the CO2 is liquefied. However established methods have the drawback that separation of CO2 and subsequent condensing is very energy intensive. The single CO2 separation method known to date which can supply liquid CO2 directly is a low-temperature or cryogenic method which is based on the fact that CO2 condenses out at low temperatures. This method also uses a lot of energy.

The known methods therefore have a comparatively high energy requirement in common, resulting in poor overall efficiency of the power station.

SUMMARY OF THE INVENTION

The object of the invention is therefore to disclose a method and a device for a power station for condensing a working medium, in particular for condensing CO2, with the intention of improving the energy balance of existing power stations using plants for condensing CO2. Building on this it is a further object of the invention to disclose a device and a method for separating CO2 from the working medium.

These objects are achieved by the inventions disclosed in the independent claims. Advantageous developments emerge from the dependent claims.

With the method according to the invention CO2 is cryogenically separated in liquid form from a working medium, in particular from a flue gas of a power station, and thus rendered transportable. Thermoacoustic machines are used here to compress and cool the flue gas. The particular advantage of the method and device lies in the fact that, by using the thermoacoustic effect, the waste heat from the power station is used to produce power P for a compressor and/or to produce cold to condense the working medium.

With what is known as the thermoacoustic effect first of all sound waves are produced in a heat transfer medium by a source of sound, for example via a loudspeaker, as is described for example in DE 43 03 052 A1. The heat transfer medium is located in a resonance tube in whose longitudinal direction the sound waves are radiated. The thermoacoustic effect accordingly substantially consists in a temperature gradient being produced between certain positions in the longitudinal direction of the tube. Heat can be dissipated to the environment or heat absorbed from the environment by way of suitable heat exchangers which are arranged at precisely these positions.

The thermoacoustic effect may be reversed such that for example by way of appropriate heat exchangers a temperature gradient is produced, resulting in pressure variations being triggered in the heat transfer medium.

FIG. 1 schematically shows two possibilities for using the thermoacoustic effect. In FIG. 1 a power P is produced in a device for producing power 130, as has been briefly described above, in that media, which are at different temperatures, flow through a first heat exchanger 110 and a second heat exchanger 120 of a first thermoacoustic machine 100. In FIG. 1 b on the other hand a second thermoacoustic machine 200 operates in a manner known per se as a cooling machine such that a high-temperature medium flows through a third heat exchanger 210 while a device for supplying power 230 produces pressure variations in the heat transfer medium of the second thermoacoustic machine. The result of this is that a medium flowing through a fourth heat exchanger 220 is cooled owing to the thermoacoustic effect.

The present invention uses the thermoacoustic effect to produce mechanical or electrical power such that pressure variations are produced in a heat transfer medium in a first thermoacoustic machine via a first heat exchanger, through which a high-temperature medium flows, and a second heat exchanger, through which a cooler medium flows. The hot medium flowing through the first heat exchanger is advantageously taken from the waste heat of the power station. The waste heat from the power station can be removed downstream of a power station burner and/or turbine. What is involved in particular here is the hot flue gas and/or steam from the power station. The medium flowing through the second heat exchanger can be provided by conventional coolants, i.e. cooling water or cooling air.

The pressure variations in the heat transfer medium act on a device for producing power 130 which includes a component which is set in motion by the pressure variations. In the simplest case this can be a piston which in a cylinder performs a linear movement corresponding to the pressure variations, which movement is converted, for example via a crankshaft, into a rotation. The device for supplying power 230 can in principle be constructed like the device for producing power, with the difference that the piston or the crankshaft in the case of the device for supplying power 230 is driven from the outside, i.e. a power P is supplied.

The power P thus produced can be transferred in the form of mechanical or electrical power. In the present application for condensing a working medium the power is transmitted to a compressor which compresses the working medium. Optimally solely the power that can be produced by the first thermoacoustic machine is sufficient to drive the compressor. Otherwise it is conceivable to activate an additional power source to supply the compressor.

Alternatively or in addition to the use of the first thermoacoustic machine, the present invention uses the thermoacoustic effect in a cooling plant, as described in connection with FIG. 1 b. In this case the hot medium flowing through the third heat exchanger 210, as in the case of the first heat exchanger 110, consists of the hot flue gases and/or steam from the waste heat of the power station. The medium flowing through the fourth heat exchanger is the working medium already compressed in the compressor and which is cooled in the fourth heat exchanger.

The invention accordingly provides the particular advantage that the energy requirement or the energy balance of an entire complex comprising power station and a plant for separating or condensing CO2 is improved as the energy required for compressing and/or cooling the working medium containing the CO2 is removed from the waste heat of the power station that is otherwise unused.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention emerge from the exemplary embodiment described hereinafter, and with reference to the drawings, in which:

FIG. 1 a shows a first potential use of the thermoacoustic effect,

FIG. 1 b shows a second potential use of the thermoacoustic effect,

FIG. 2 shows a device according to the invention for condensing a working medium and

FIG. 3 shows a further device according to the invention for condensing a working medium.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a device for condensing a working medium, in particular for condensing CO2. In a pipe 1 coming from a power station 10 the working medium, which in the present exemplary embodiment comprises a plant for condensing CO2 from flue gases and CO2, is guided to a flue gas cooler 20. From there the flue gas passes via a pipe 2 into a compressor 30 where it is compressed. The compressed working medium is then supplied via a pipe 3 to a dryer 40 to remove water in particular from the working medium, in order to then arrive via a pipe 4 in a cooling plant 50. The cooling plant 50 comprises inter alia a heat exchanger 220, hereinafter called the fourth heat exchanger 220, through which the working medium passes and is cooled in the process. Following the cooling plant 50 the working medium arrives via a pipe 5 in a further cooling plant 60 and from there via a pipe 6 in a separator 70. Liquid CO2 is separated from residual gases low in CO2 in the separator 70.

Standard assemblies known from the prior art can be used for most of the assemblies in the above-described device for condensing CO2, i.e. as flue gas cooler 20, as compressor 30, as dryer 40, as further cooling plant 60 and as separator 70. These assemblies and their modes of operation are not the subject matter of the present invention and will therefore not be described further.

According to the invention a first thermoacoustic machine 100 is used to produce the power P required by the compressor 30 to compress the working medium. A second thermoacoustic machine 200 is used in addition or as an alternative hereto in the cooling plant 50.

The first thermoacoustic machine 100 comprises a first container 160 which can be constructed for example as a resonance tube and which comprises a first heat exchanger 110, a second heat exchanger 120 and a first heat transfer medium 170, for example air. The first 110 and second heat exchangers 120 are in thermal contact via the first heat transfer medium 170.

A first medium accordingly flows through the first heat exchanger 110 and a second medium flows through the second heat exchanger 120, the temperature of the first medium being higher than the temperature of the second medium. In particular, according to the invention the first heat exchanger 110 is supplied via a feeding pipe 111 with the waste heat from the power station 10, in particular with hot flue gas and/or steam. For this purpose the feeding pipe 111 is connected to a waste heat pipe 11 of the power station 10, it being possible to remove waste heat from the power station 10 downstream of a burner and/or a turbine of the power station 10. The second heat exchanger 120 is supplied with a coolant, in particular with cooling air or cooling water, via a feeding pipe 121.

The temperature gradient between the first 110 and second heat exchangers 120, owing to the thermoacoustic effect therein, results in pressure variations being produced in the first heat transfer medium 170 in the resonance tube 160. A device for producing power 130 is coupled to the first thermoacoustic machine 100 in such a way that these pressure variations can act on the device for producing power 130.

The device for producing power 130 can comprise for example a piston 131, a cylinder 132, and a crankshaft 134, the cylinder 132 being attached to an opening 180 in the resonance tube 160, so the pressure variations produce forces on the piston 131. The piston 131 consequently moves in the direction of the arrow 133, drives the crankshaft 134 and thus produces a power P which is finally transmitted via a pipe 7 to the compressor 30. It is conceivable in this connection to operate a generator (not shown) for power generation by means of the crankshaft 134 and to supply the compressor 30 with the power produced. In this case the pipe 7 is a current-carrying connection. Alternatively the crankshaft 134 can be mechanically connected to a shaft of the compressor 30, so the compressor is driven directly. In this case the pipe 7 is a mechanical connection between the device for producing power 130 and the compressor 30. It may be generally be stated that the device for producing power 130 is capable of absorbing the pressure variations in the resonance tube 160 and of converting them into a power P. Devices of this kind for producing power are known to a person skilled in the art. By way of example a linear compressor can be used which combines the device for producing power 130 and the compressor 30. Means and methods of transmitting the produced power P to the compressor 30 are also known to a person skilled in the art.

Additional power P′ can optionally be supplied to the compressor 30 via an optional feeding pipe 8 if the power P produced by the first thermoacoustic effect is not sufficient to adequately compress the air to be separated.

Alternatively or in addition to the use of the first thermoacoustic machine 100, a second thermoacoustic machine 200 can be used as the cooling machine. The second thermoacoustic machine 200 is used to cool the working medium compressed in the compressor 30 and liberated of water in the dryer 40. For this purpose the second thermoacoustic machine 200 has a second container or a second resonance tube 260 which includes a third heat exchanger 210, the fourth heat exchanger 220 already introduced above, and a second heat transfer medium 270, for example air. The third heat exchanger 210 is in thermal contact with the fourth heat exchanger 220 via the second heat transfer medium 270.

A device for producing power 230 is coupled to the second thermoacoustic machine 200, or its resonance tube 260, for example via an opening 280 in such a way that pressure variations can be produced in the second heat transfer medium 270, or existing pressure variations can be intensified. The device for producing power 230 can comprise, for example, a piston 231 and a cylinder 232, the cylinder 232 being attached to the opening 280 in the resonance tube 260. The piston 231 is moved in the direction of the arrow 233, for example via a crankshaft 234, to produce the pressure variations, the crankshaft 234 being driven in any desired manner. Appropriate devices for driving a crankshaft, for example with the aid of a motor, are sufficiently known.

Alternatively the device for supplying power 230 can also be constructed as a loudspeaker or the like. It is essential only that pressure variations can be produced in the second heat transfer medium 270.

A third, high-temperature medium flows through the third heat exchanger 210. In particular, according to the invention the third heat exchanger 210, like the first heat exchanger 110, is supplied via a feeding pipe 211 with the waste heat from the power station 10, in particular with hot flue gas and/or steam. The feeding pipe 211 is connected to the waste heat pipe 11 of the power station 10 for this purpose.

The working medium flows through the fourth heat exchanger 220. The thermoacoustic effect described with FIG. 1 b cools the working medium in the fourth heat exchanger 220. The compressed and cooled working medium present at the output to the fourth heat exchanger 220 is optionally guided via the additional cooling plant 60 to the separator 70 where, finally, the liquid CO2 is obtained at an output 9 of the separator 70. Residual gases that are low in CO2 can be removed at a second output of the separator 70.

Cooling in the cooling plant 50 can be omitted in condensing CO2 depending on the composition of the flue gases. Provided that other combustion products, such as sulphur oxides (SO_(x)) and/or nitrogen (N₂), originally present in the flue gases have already been separated CO2 can be condensed using the device shown simplified in FIG. 3. Specifically it is required that the flue gases are allowed to contain less than about 5% nitrogen (N2) and sulphur oxides (SO_(x)) in the low ppm range. This requirement is also met in the case of what are known as oxyfuel methods where a fuel is burnt with pure oxygen, so the flue gases contain very high CO2 concentrations with minimal “contaminants” as a result of other combustion products, substantially simplifying CO2 separation and CO2 condensing.

In FIG. 3 a working medium or flue gas present at a point A and which meets the above-expressed requirement is guided into a dryer 40 to remove water in particular from the working medium. From there the working medium arrives in a compressor 30 which compresses the working medium. The power P required for this is produced according to the invention with the aid of a thermoacoustic machine 100′ in a device for producing power 130. The thermoacoustic machine 100′ and the device for producing power 130 are shown only symbolically in FIG. 3. However the thermoacoustic machine 100′ is constructed exactly like the first thermoacoustic machine 100 in FIG. 2 and operates like it. The same applies to the device for producing power 130. The working medium leaving the compressor 30 can optionally be compressed further by an additional compressor 35. Finally liquid CO2 is present at point B.

Ideally CO2 separation or CO2 condensing can take place using the solution according to the invention without an additional supply of energy. In principle the solution according to the invention allows energy consumption to be significantly reduced when separating or condensing CO2. 

1-18. (canceled)
 19. A method for condensing a working medium of a power station, comprising: producing a power to a compressor by a first thermoacoustic machine; compressing the working medium by the compressor; generating a cold to a cooling device by a second thermoacoustic machine; and cooling the compressed working medium in the cooling device.
 20. The method as claimed in claim 19, wherein a waste heat of the power station is supplied to the first thermoacoustic machine or the second thermoacoustic machine.
 21. The method as claimed in claim 20, wherein the first thermoacoustic machine comprises a first heat exchanger and a second heat exchanger, wherein the first heat exchanger is thermally contacted with the second heat exchanger via a first heat transfer medium, and wherein a power generation device converts a pressure variation produced in the first heat transfer medium by a thermoacoustic effect into the power to the compressor.
 22. The method as claimed in claim 21, wherein the waste heat is supplied to the first heat exchanger and a coolant is supplied to the second heat exchanger.
 23. The method as claimed in claim 21, wherein the power is transmitted to the compressor via a pipe.
 24. The method as claimed in claim 19, wherein the second thermoacoustic machine comprises a third heat exchanger and a fourth heat exchanger, wherein the third heat exchanger is thermally contacted with the forth heat exchanger via a second heat transfer medium, and wherein the working medium passes through the fourth heat exchanger and is cooled by a thermoacoustic effect.
 25. The method as claimed in claim 24, wherein the waste heat is supplied to the third heat exchanger and a power supply device produces a pressure variation in the second heat transfer medium or intensifies an existing pressure variation.
 26. The method as claimed in claim 19, wherein the working medium comprises CO2 and is liquefied by the condensing, and wherein a separator separates the liquefied working medium into liquid CO2 and a residual medium that is low in CO2.
 27. A device for condensing a working medium of a power station, comprising: a compressor that compresses the working medium; a cooling device that cools the compressed working medium; a first thermoacoustic machine that produces a power to the compressor for compressing the working medium; and a second thermoacoustic machine that produces a cold to the cooling device for cooling the compressed working medium.
 28. The device as claimed in claim 27, wherein a waste heat pipe of the power station is connected to the first thermoacoustic machine or the second thermoacoustic machine.
 29. The device as claimed in claim 28, wherein the first thermoacoustic machine comprises a first heat exchanger and a second heat exchanger, wherein the first heat exchanger is thermally contacted with the second heat exchanger via a first heat transfer medium, and wherein a power generation device is coupled to the first thermoacoustic machine and converts a pressure variation produced in the first heat transfer medium by a thermoacoustic effect into the power to the compressor.
 30. The device as claimed in claim 29, wherein the waste heat is supplied to the first heat exchanger via a first feeding pipe connected to the waste heat pipe and a coolant is supplied to the second heat exchanger via a second feeding pipe.
 31. The device as claimed in claim 29, wherein the power generation device is jointly constructed with the compressor as a linear compressor and comprises components to produce the power to the compressor via the pressure variation.
 32. The device as claimed in claim 29, wherein the power generation device is connected to the compressor via a pipe to transmit the power.
 33. The device as claimed in claim 27, wherein the second thermoacoustic machine comprises a third heat exchanger and a fourth heat exchanger, wherein the third heat exchanger is thermally contacted with the forth heat exchanger via a second heat transfer medium, and wherein the working medium passes through the fourth heat exchanger and is cooled by a thermoacoustic effect.
 34. The device as claimed in claim 33, wherein the waste heat is supplied to the third heat exchanger via a third feeding pipe connected to the waste heat pipe, and wherein a power supplying device is coupled to the second thermoacoustic machine and produces a pressure variation in the second heat transfer medium or intensifies an existing pressure variation.
 35. The device as claimed in claim 33, wherein an input of the fourth heat exchanger is connected to an output of the compressor.
 36. A device for CO2 separation of a working medium of a power station, comprising: a compressor that compresses the working medium; a cooling device that cools the compressed working medium; a first thermoacoustic machine that produces a power to the compressor for compressing the working medium; a second thermoacoustic machine that produces a cold to the cooling device for cooling the compressed working medium to a liquefied working medium; and a separator that separates the liquefied working medium into liquid CO2 and a residual medium low in CO2. 